Microchip Technology MA240017 Data Sheet
2008-2011 Microchip Technology Inc.
DS39927C-page 127
PIC24F16KA102 FAMILY
EXAMPLE 15-1:
PWM PERIOD AND DUTY CYCLE CALCULATIONS
(
TABLE 15-1:
EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 4 MIPS (F
CY
= 4 MHz)
(
TABLE 15-2:
EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 16 MIPS (F
CY
= 16 MHz)
PWM Frequency
7.6 Hz
61 Hz
122 Hz
977 Hz
3.9 kHz
31.3 kHz
125 kHz
Timer Prescaler Ratio
8
1
1
1
1
1
1
Period Register Value
FFFFh
FFFFh
7FFFh
0FFFh
03FFh
007Fh
001Fh
Resolution (bits)
16
16
15
12
10
7
5
Note 1:
Based on F
CY
= F
OSC
/2; Doze mode and PLL are disabled.
PWM Frequency
30.5 Hz
244 Hz
488 Hz
3.9 kHz
15.6 kHz
125 kHz
500 kHz
Timer Prescaler Ratio
8
1
1
1
1
1
1
Period Register Value
FFFFh
FFFFh
7FFFh
0FFFh
03FFh
007Fh
001Fh
Resolution (bits)
16
16
15
12
10
7
5
Note 1:
Based on F
CY
= F
OSC
/2; Doze mode and PLL are disabled.
1.
Find the Timer Period register value for a desired PWM frequency of 52.08 kHz, where F
OSC
= 8 MHz with PLL
(32 MHz device clock rate) and a Timer2 prescaler setting of 1:1.
T
T
CY
= 2 * T
OSC
= 62.5 ns
PWM Period = 1/PWM Frequency = 1/52.08 kHz = 19.2
s
PWM Period = (PR2 + 1) • T
CY
• (Timer 2 Prescale Value)
19.2
s = (PR2 + 1) • 62.5 ns • 1
PR2 = 306
2.
Find the maximum resolution of the duty cycle that can be used with a 52.08 kHz frequency and a 32 MHz
device clock rate:
PWM Resolution = log
device clock rate:
PWM Resolution = log
10
(F
CY
/F
PWM
)/log
10
2) bits
= (log
10
(16 MHz/52.08 kHz)/log
10
2) bits
= 8.3 bits
Note 1:
Based on T
CY
= 2 * T
OSC
; Doze mode and PLL are disabled.